EP3231057B1 - Method and device for detecting an overcharging of an accumulator of a battery - Google Patents

Description

The present invention relates to the detection of an overload of an accumulator of a battery comprising a set of parallel branches, each branch comprising accumulators arranged in series.

A battery charging operation comprising such accumulators is carried out by applying a charging voltage across the terminals of the branches of the battery.

Certain accumulators, in particular those comprising Lithium, do not support overcharging. Indeed, a Lithium-ion accumulator subjected to an overcharge gives rise to a phenomenon called "venting" corresponding to a release of gas (outside the mechanical envelope of the accumulator, which can be accompanied by a fine cloud of electrolyte, and lead to degradation (heating, overpressure, even explosion).

A battery charging operation comprising such accumulators must therefore be associated with monitoring the battery to detect possible overcharging and very quickly stop charging.

Traditionally, the voltage at the terminals of accumulators is monitored, or even controlled, by a battery management system, called BMS (“Battery Management System” in English) which can trigger an alarm or a charge cut if the voltage of an accumulator becomes too high. However, malfunctions occur in these BMS systems, due to the large number of electronic components required and it is therefore desirable to have various monitoring solutions to avoid common modes of failure.

Other solutions to prevent malfunctions in the batteries are based on the measurement of currents flowing in the branches, as described for example in the document EP13008739 A2 or in the document US 2011/298626 A1 .

However, these solutions of the prior art give rise to interruptions or alarms in cases where no accumulator is actually overcharged.

• collecter les mesures des courants circulant dans les branches de la batterie ;
• identifier au moins un écart de courant dans une branche dudit ensemble de branches par rapport à au moins une autre branche dudit ensemble de branches en fonction des mesures de courant collectées ;
• déterminer un niveau d'état de charge de ladite branche ; et
• détecter une surcharge d'un accumulateur dans ladite branche en fonction d'au moins ledit écart de courant identifié et du niveau d'état de charge déterminé.

To this end, according to a first aspect, the invention proposes a method for detecting an overcharge of an accumulator of a battery comprising a set of parallel branches, each branch comprising accumulators arranged in series, said method being characterized in what it includes the following steps:

• collect the measurements of the currents flowing in the branches of the battery;
• identifying at least one current deviation in a branch of said set of branches relative to at least one other branch of said set of branches according to the collected current measurements;
• determining a state of charge level of said branch; and
• detecting an overload of an accumulator in said branch as a function of at least said identified current difference and of the determined state of charge level.

The present invention makes it possible to limit the erroneous overload detection cases identified with the solutions of the prior art.

In particular, the present invention makes it possible to distinguish the differences in current between branches due to an overcharging of an accumulator in a branch and the differences in current due to branches of the battery having different storage capacities, thus avoiding the problems. , encountered in the prior art, untimely disconnections of such a branch when it does not include an overcharged accumulator.

• la détection d'une surcharge comprend le test d'au moins une condition relative à l'écart de courant identifié, ladite condition à tester relative à l'écart de courant identifié étant fonction du niveau d'état de charge déterminé ;
• on calcule une différence entre le courant mesuré dans ladite branche (B1,..., BN) et un courant de référence déterminé en fonction d'au moins le courant mesuré dans l'autre branche ;
• ladite différence est comparée à un seuil ;
• une surcharge d'un accumulateur dans ladite branche est détectée en fonction du résultat de ladite comparaison et du niveau de charge déterminé ;
• on identifie un premier écart de courant dans ladite branche à un premier temps en fonction d'un premier seuil d'écart de courant, on identifie un deuxième écart de courant dans ladite branche à un deuxième temps en fonction d'un deuxième seuil d'écart de courant distinct du premier seuil d'écart de courant, et une surcharge d'un accumulateur dans ladite branche est détectée en fonction dudit premier écart de courant, dudit deuxième écart de courant et du niveau d'état de charge déterminé ;
• on distingue au moins une première plage de niveaux d'état de charge et une deuxième plage, postérieure à ladite première plage, de niveaux d'état de charge, et si un niveau d'état de charge de la branche est déterminé dans la deuxième plage, une surcharge d'un accumulateur dans ladite branche est détectée si l'écart de courant identifié dans ladite branche franchit d'abord un premier seuil et ultérieurement franchit un deuxième seuil, le signe des premier et deuxième seuil étant opposés ;
• le premier seuil est égal à l'opposé du deuxième seuil ;
• une surcharge d'un accumulateur dans ladite branche est détectée, pour un niveau d'état de charge déterminé dans la première plage, dès que l'écart de courant identifié dans ladite branche franchit le premier seuil.

In embodiments, the method for detecting an overload of an accumulator of a battery according to the invention further comprises one or more of the following characteristics:

• detecting an overload comprises testing at least one condition relating to the identified current deviation, said condition to be tested relating to the identified current deviation being a function of the determined state of charge level;
• a difference is calculated between the current measured in said branch (B1, ..., BN) and a reference current determined as a function of at least the current measured in the other branch;
• said difference is compared to a threshold;
• an overload of an accumulator in said branch is detected as a function of the result of said comparison and of the determined charge level;
• a first current difference in said branch is identified at a first time as a function of a first threshold of current difference, a second current difference is identified in said branch at a second time as a function of a second threshold of current difference distinct from the first current difference threshold, and an overload of an accumulator in said branch is detected as a function of said first current difference, said second current difference and the determined state of charge level;
• at least a first range of state of charge levels and a second range, subsequent to said first range, of state of charge levels are distinguished, and if a state of charge level of the branch is determined in the second range, an overload of an accumulator in said branch is detected if the current deviation identified in said branch first crosses a first threshold and subsequently crosses a second threshold, the sign of the first and second threshold being opposite;
• the first threshold is equal to the opposite of the second threshold;
• an overload of an accumulator in said branch is detected, for a state of charge level determined in the first range, as soon as the current difference identified in said branch crosses the first threshold.

According to a second aspect, the present invention provides a computer program for the detection of an overcharge of an accumulator of a battery comprising a set of parallel branches each comprising accumulators arranged in series, said product computer program comprising software instructions which, when executed on calculation means, implement the steps of a method according to the first aspect of the invention.

According to a third aspect, the present invention provides a device for detecting an overcharge of a battery accumulator comprising a set of parallel branches each branch comprising accumulators arranged in series, said device being characterized in that it is adapted to collect the measurements of the currents flowing in the branches of the battery, to identify at least one current difference in one branch of said set of branches relative to at least one other branch of said set of branches as a function of the collected current measurements, to determine a state of charge level of said branch; and for detecting an overload of an accumulator in said branch as a function of at least said identified current deviation and of the determined state of charge level.

• la figure 1 représente une vue d'un système de batterie dans un mode de réalisation de l'invention ;
• la figure 2 est une vue d'un graphe représentant l'évolution de la tension d'un accumulateur d'une batterie en fonction de l'état de charge de l'accumulateur dans un mode de réalisation de l'invention ;
• la figure 3 est un organigramme d'étapes d'un procédé dans un mode de réalisation de l'invention.

These characteristics and advantages of the invention will appear on reading the description which follows, given solely by way of example, and made with reference to the appended drawings, in which:

• the figure 1 shows a view of a battery system in an embodiment of the invention;
• the figure 2 is a view of a graph representing the evolution of the voltage of an accumulator of a battery as a function of the state of charge of the accumulator in an embodiment of the invention;
• the figure 3 is a flow diagram of steps of a method in an embodiment of the invention.

The figure 1 is a view of a battery system 10 in one embodiment of the invention.

The battery system 10 comprises a battery comprising N packs, also called branches, B1, B2, ... BN, and arranged in parallel.

N is an integer greater than or equal to 2.

The voltage between the positive and negative terminals of the battery is equal to the voltage at the terminals of each branch.

Each branch has accumulators 11 connected in series.

For example, the number of accumulators in a branch is equal to M, M is an integer greater than or equal to 2.

In known manner, an accumulator is an elementary energy brick suitable for storing energy.

The battery system 10 includes an overload monitoring device 1.

In one embodiment, the battery 10 is of the Li-ion type and the accumulators are of LFP (Lithium Iron Phosphate) technology.

The battery 10 is for example intended for the electrical supply of a submarine.

In the embodiment considered, the battery system 10 further comprises devices for controlling the voltage of the accumulators, referenced 2 ₁ , 2 _i , ..., 2 _N.

Each device 2 _i , for controlling the voltage of the accumulators is associated with a respective branch Bi and is adapted to measure and control the voltage across each accumulator 11 of the branch Bi, i = 1 to N.

For example, the device 2i for checking the voltage of the accumulators is suitable for balancing the operating voltages at the terminals of the accumulators in series in the branch Bi so that all the accumulators of the branch Bi terminate their charge synchronously. In fact, during charging, not all of the accumulators are charged at the same speed due to the disparities in intrinsic characteristics between accumulators. The device 2i for checking the voltage of the accumulators then discharges the most charged accumulators of the branch Bi, and as the charges of the accumulators within the branch Bi equalize.

The device 2i for checking the voltage of the accumulators is further adapted for, when the voltage of an accumulator of the branch Bi reaches the upper limit voltage of the accumulator, initiating a charging stop of the branch Bi of the accumulator (in other embodiments, only a stop of charging of the accumulator is triggered) for example by actuation of switches (not shown).

The battery system 10 further comprises current sensors CC1, CC2, ..., CCN.

The current sensor CCi is suitable for regularly measuring the current flowing in the branch Bi of the battery system 10, i = 1 to N.

The figure 2 represents the curve of the evolution of the voltage V of an accumulator 11 as a function of the state of charge E _ch of the accumulator.

The state of charge indicates the quantity of energy stored in relation to the maximum quantity that can be stored by the accumulator and corresponding to a nominal operating voltage V2. (100% state of charge means that the maximum charging voltage of the accumulator fixed by the manufacturer has been reached and which must not be exceeded under penalty of entering a hazardous operating zone. Physically, when this maximum voltage is reached, for LFP, this means that all the lithium ion insertion sites are filled. If we go above, we start to deteriorate the accumulator and its electrodes)

The state of charge of the accumulator is for example expressed as a percentage.

The amount of energy, stored or storable, of a battery is for example measured in watt-hours (Wh) and it corresponds to a capacity of the battery, for example measured in ampere-hours (Ah).

The value V1 represents the minimum operating voltage value of the accumulator, V2 represents the maximum charging voltage value of the accumulator, while V3 represents the saturation voltage value of the accumulator during an overcharge.

In the case of a Li-ion battery of LFP technology, typically: V1 = 2.5V, V2 = 3.6 V and V3 = 5V.

The curve shown in figure 2 has a voltage plateau, area in which the slope of the voltage as a function of the state of charge is very low, then the voltage rises abruptly in the last 5 percent of charge before reaching the maximum charge voltage V2.

If the charge continues beyond this, the accumulator reaches saturation at the high limit voltage V3, a voltage at which it may remain more or less long before going on "venting", depending on the charge regime. The lower it is, the longer it will take for the overcharged accumulator before the “venting” phenomenon occurs.

• il sature à la tension V3 ; et
• il continue de voir un courant de charge, i.e. les autres accumulateurs en série avec lui présentent des tensions inférieures aux tensions des accumulateurs des autres branches du fait de la mise en parallèle des packs.

For there to be an overload on an accumulator 11 in series within a Bi branch, this accumulator 11 must be in the following conditions:

• it saturates at voltage V3; and
• it continues to see a charging current, ie the other accumulators in series with it have voltages lower than the voltages of the accumulators of the other branches due to the paralleling of the packs.

It will be noted that if an accumulator 11 in a branch Bi is overcharged, this means that the device 2 _i , for checking the voltage of the accumulators in the branch Bi of the accumulator 11 has not worked properly and has not carried out a balancing, nor triggered a charge stop when the battery voltage reached the high limit voltage V3.

In one embodiment of the invention, the space (V, Ech) of the accumulator is subdivided into distinct zones.

Each zone corresponds to a charging phase.

The charging phases are defined by one or more respective ranges of state of charge values.

• la zone I associée à un état de charge de l'accumulateur compris entre [0, Ech₁] correspond à un début de charge ;
• la zone II associée à un état de charge de l'accumulateur compris entre [Ech₁, Ech₃] correspond à une fin de charge ;
• la zone III associée à un état de charge de l'accumulateur supérieur à Ech₃ correspond à une surtension, et donc à terme à une surcharge ; sur la figure 2, la zone de surcharge, correspondant à l'atteinte par la tension de l'accumulateur de la saturation en tension V3 est indiquée par des rayures.

In this case, three zones I, II and III are considered and are identified on the figure 2 :

• zone I associated with a state of charge of the accumulator comprised between [0, Ech ₁ ] corresponds to a start of charge;
• zone II associated with a state of charge of the accumulator comprised between [Ech ₁ , Ech ₃ ] corresponds to an end of charge;
• zone III associated with a state of charge of the accumulator greater than Ech ₃ corresponds to an overvoltage, and therefore ultimately to an overload; on the figure 2 , the overload zone, corresponding to the reaching by the voltage of the accumulator of the saturation in voltage V3 is indicated by stripes.

In the case of a Li-ion battery with LFP technology, Ech ₁ = 90%, Ech ₃ = 100%.

In one embodiment, the state of charge of each branch of the battery is also considered, and similarly to what has been described above with reference to accumulators, charging phases of a battery branch are defined. by one or more respective ranges of state of charge values.

• la zone ZI associée à un état de charge d'une branche compris entre [0, Ech₁] correspond à un début de charge ;
• la zone ZII associée à un état de charge d'une branche compris entre [Ech₁, Ech₃] correspond à une fin de charge ;
• la zone III associée à un état de charge d'une branche, supérieur à Ech₃ correspond à une surtension, et donc à terme à une surcharge.

In the embodiment, three zones ZI, ZII and ZIII are considered:

• zone ZI associated with a state of charge of a branch comprised between [0, Ech ₁ ] corresponds to a start of charge;
• zone ZII associated with a state of charge of a branch comprised between [Ech ₁ , Ech ₃ ] corresponds to an end of charge;
• zone III associated with a state of charge of a branch, greater than Ech ₃ corresponds to an overvoltage, and therefore ultimately to an overload.

In the embodiment considered, the overload monitoring device 1 is adapted to implement the set of steps 100 described below with reference to the figure 3 .

In one embodiment, the overload monitoring device 1 comprises a memory and a microprocessor. The memory stores software instructions which, when executed by the microprocessor of the overload monitoring device 1, implement the set of steps 100.

The set of steps 100 is for example repeated by the overload monitoring device 1 at each instant of iteration T _n = T ₀ + n / F0 during the charging of the battery, where T ₀ is the start time charging the battery.

In a step 101, the overload monitoring device 1 is adapted to collect in real time the measurements, carried out by the current sensors CCi, i = 1 to N, of the currents in the branches Bi and the overload monitoring device 1 is also suitable for determining the current state of charge of the battery or of each Bi branch.

In a step 102, the overload monitoring device 1 is adapted to identify a current difference in a branch with respect to at least one other of said branches according to the current measurements collected in step 101 and for, according to the difference in current identified and the determined state of charge level (of the battery or of each Bi branch), detect the presence or absence of an overload of an accumulator in the Bi branch.

In a step 103, in the case where a branch Bi ₀ has been detected as being overloaded in step 102, the overload monitoring device 1 is adapted to trigger the stopping of the load in the branch Bi ₀ . Such a charging stop in the Bi ₀ branch is triggered for example by emitting an alarm or by actuating switches (not shown) disconnecting the Bi ₀ branch from the terminals for applying the battery charging voltage.

In one embodiment, the accumulators are balanced before recharging so that they are in a state of charge assumed to be identical and known, the evaluation of the state of charge being carried out by means of the current sensors. For example, in a preliminary step, before recharging the battery, the accumulators 11 of the battery are balanced at a fixed common low discharge level (for example corresponding to a voltage level V1) by the control devices 2 _i of the battery voltage. Thus in one embodiment, the overload monitoring device 1 is adapted to determine the current state of charge in step 101 by taking it equal to the state of charge of the battery, calculated by counting the total of the amperes stored by the battery, according to the current measurements collected from T ₀ .

Such a method makes it possible to reduce the risk of detecting overloads when there is none.

In one embodiment, the following operations are carried out by the overload monitoring device 1 in step 102 at the time of iteration T _n .

To identify a different distribution of current between the branches, the overload monitoring device 1 calculates the value of a reference current I _{ref_n} equal to the sum of the currents commonly measured in the N branches divided by the number N of branches.

$${\mathrm{\Delta I}}_{\mathrm{Bi}\_\mathrm{n}}={\mathrm{I}}_{\mathrm{ref}\_\mathrm{n}}-{\mathrm{I}}_{\mathrm{Bi}\_\mathrm{n}}.$$

Then the overload monitoring device 1 calculates the difference ΔI _{Bi_n} between the measurement of the current in the branch Bi commonly collected in step 100, called I _{Bi_n} , and the reference current I _{ref_n} , for i = 1 to N, ie : $${\mathrm{I}}_{\mathrm{ref}\_\mathrm{not}}=\left({\mathrm{\Sigma }}_{\mathrm{i}=1\mathrm{at}\mathrm{NOT}}{\mathrm{I}}_{\mathrm{Bi}\_\mathrm{not}}\right)/\mathrm{NOT};$$

$${\mathrm{\Delta I}}_{\mathrm{Bi}\_\mathrm{not}}={\mathrm{I}}_{\mathrm{ref}\_\mathrm{not}}-{\mathrm{I}}_{\mathrm{Bi}\_\mathrm{not}}.$$

• cond(I) : si l'état de charge déterminé à l'étape 101 de l'instant d'itération T_n est égal à ZI et que ΔI_{Bi_n} > Δ_seuil, alors il existe un accumulateur 11 en surcharge dans la branche Bi ;
• cond(II) : s'il est détecté, au cours de la charge dans la zone ZII, le dépassement du seuil Δ_seuil, puis le passage en-dessous du seuil -Δ_seuil, alors il existe un accumulateur 11 en surcharge dans la branche Bi ; la mise en œuvre de la condition cond(II) est par exemple la suivante : si l'état de charge déterminé à l'étape 101 de l'instant d'itération T_n est égal à ZII, que ΔI_{Bi_n}, < - Δ_seuil et qu'il a été déterminé au cours de la charge dans la zone ZII et à un instant antérieur, par exemple nommé T_m(T_m<T_n) que ΔI_{Bi_m} > Δ_seuil, alors il existe un accumulateur 11 en surcharge dans la branche Bi.

Then the overload monitoring device 1 tests the following conditions cond (l) and cond (II) for i = 1 to N and thus detects the presence or absence of an overload of an accumulator in a branch:

• cond (I): if the state of charge determined in step 101 of the iteration instant T _n is equal to ZI and that ΔI _{Bi_n} > Δ _threshold , then there is an accumulator 11 in overload in the branch Bi ;
• cond (II): if it is detected, during the charging in zone ZII, the exceeding of the threshold Δ _threshold , then the passage below the threshold -Δ _threshold , then there is an accumulator 11 in overload in the Bi branch; the implementation of the condition cond (II) is for example the following: if the state of charge determined in step 101 of the instant of iteration T _n is equal to ZII, that ΔI _{Bi_n} , <- Δ _threshold and that it was determined during the charging in the zone ZII and at an earlier instant, for example named T _m (T _m <T _n ) that ΔI _{Bi_m} > Δ _threshold , then there is an accumulator 11 in overload in the Bi branch.

The threshold value Δ _threshold is a positive value fixed experimentally.

Moreover it is noted that in embodiments, it may be used a Δ _threshold1 threshold value for testing the condition cond (l) and a separate threshold value, Δ _threshold2, to test the condition cond (II)) the crossing this threshold _threshold2 Δ and its opposite - Δ _threshold2. In one embodiment, separate values are taken for the positive threshold Δ _{threshold2_1} and the negative threshold - Δ _{threshold2_2} whose successive crossings are detected by the condition cond (II).

If the test of these conditions cond (l) and cond (II) for each i, i = 1 to n, does not give rise to overload detection by the overload monitoring device 1, the latter concludes that there is no overload within the battery at time T _n .

Consider the following scenarios:
Case A: an accumulator 11 in a branch Bi ₀ enters an overload in the zone ZI.

In this case, the overvoltage is generated at the Bi ₀ branch by the accumulator 11 in overload (for example greater than 1.5V), which gives the illusion to other branches that the Bi ₀ branch has a certain percentage. of charge more than they. Naturally, the current in the Bi ₀ branch will then decrease and the other branches will distribute an additional current, in total equivalent to the decrease in the current in this Bi ₀ branch. Thus, the other branches compensate for their "delay" on the Bi ₀ branch.

Case B: an accumulator 11 in a branch Bi ₀ enters an overload in the zone ZII. The Bi ₀ branch then takes a delay in its charge because the increase in voltage at its terminals, due to the overvoltage of the faulty accumulator, does not correspond to a real increase in the state of charge of the branch. Once the voltage of this accumulator reaches the saturation voltage, the branch Bi ₀ must then make up for the accumulated state of charge delay by accepting a current increase.

Case C: In zone ZIII, the other branches imposing a maximum voltage on the branch Bi ₀ , the accumulators of the branch Bi ₀ have a sufficiently high voltage to prevent the branch Bi ₀ from going beyond a voltage where an accumulator can saturate at 5V if the device 2i ₀ for checking the voltage of the accumulators has not worked.

Thus, when the state of charge is ZI, the exceeding by _threshold ΔI _{Bio_n} of the threshold value Δ _threshold is characteristic of the presence of an overcharged accumulator in the branch Bi ₀ , as described by case A.

When the state of charge is ZII and the difference between the measurement of the current in the branch Bi ₀ and the reference current I _{ref_n} , _firstly becomes greater than the first threshold equal to Δ _threshold , then less than the second threshold equal at -Δ _threshold , this means that an accumulator has not been properly balanced and that it is overcharged.

Crossing the second threshold after the first makes it possible to detect that there has been a malfunction in the voltage management of at least one accumulator. If the overload detection only took into account the crossing of the first threshold had been considered, an overload could have been reported in error if the Bi ₀ branch was overall weaker than the other branches, without this signifying that there has overcharge of an accumulator in the Bi ₀ branch.

In the case where the battery has a branch of lower capacity than the other branches, there will indeed be in zone ZII a crossing of Δ _threshold , but no subsequent crossing of -Δ _threshold , therefore the present invention will avoid an erroneous overload detection in such a case.

In an embodiment described above, the condition to be tested relating to a current difference in a Bi branch comprises the calculation of the difference between the measurement of the current in the Bi branch and a reference current equal to the average of the currents circulating in the different branches, then comparing this difference with a threshold. In other embodiments, the condition to be tested relating to a current difference in a branch Bi takes different forms, for example the reference current is chosen equal to a current flowing in another branch.

The present invention thus provides a solution for detecting overcharging problems within a battery and in particular for detecting and overcoming malfunctions of the devices for controlling the voltage of the accumulators of the battery. In one embodiment, the invention thus makes it possible to carry out overload detection on the basis of current measurements alone, and independently of measurements of voltage of the accumulators.

Claims (15)

1. An overcharge detection method for detecting an overcharging of an accumulator (11) of a battery (10) comprising a set of parallel branches (B1, ..., BN), each branch comprising accumulators disposed in series, said method comprising the following steps:

   - (i) collecting the measurements of the currents flowing through the branches of the battery;

   - (ii) identifying at least one variation in current in one branch of the said set of branches with respect to at least one other branch of the said set of branches as a function of the measurements of current collected;

   - (iii) determining a level of state of charge of the said branch; and

   - (iv) detecting an overcharging of an accumulator in the said branch as a function of at least the said variation in current identified and of the level of state of charge determined.
2. An overcharge detection method for detecting an overcharging of an accumulator (11) according to claim 1, in which the detection of an overcharging includes the testing of at least one condition relative to the variation in current identified, the said condition to be tested relative to the variation in current identified being a function of the level of state of charge determined.
3. An overcharge detection method for detecting an overcharging of an accumulator (11) according to claim 1 or claim 2, based on which:

   - a difference between the current measured in the said branch (B1, ..., BN) and a reference current determined as a function of at least the current measured in the other branch is calculated;

   - the said difference is compared to a threshold value; and

   - an overcharging of an accumulator in the said branch is detected based on the result of the said comparison and the level of state of charge determined.
4. An overcharge detection method for detecting an overcharging of an accumulator (11) according to any one of the preceding claims, in which a first variation in current identified in the said branch (B1,..., BN) at a first time instant is compared with a first threshold value of current variation, a second variation in current identified in the said branch at a second time instant is compared with a second current variation threshold value that is distinct from the first current variation threshold value, and an overcharging of an accumulator in the said branch is detected as a function of the said first variation in current, of the said second variation in current and of the level of state of charge determined.
5. An overcharge detection method for detecting an overcharging of an accumulator (11) according to any one of the preceding claims, based on which one can distinguish at least a first range (ZI) of state of charge levels and a second range (ZII), subsequent to the said first range, of state of charge levels, and if a state of charge level of the branch is determined to be in the second range, an overcharging of an accumulator in the said branch is detected if the variation in current identified in the said branch firstly surpasses a first threshold and subsequently surpasses a second threshold, the first and second threshold values having opposite signs.
6. An overcharge detection method for detecting an overcharging of an accumulator (11) according to claim 5, the first threshold value being equal to the opposite of the second threshold value.
7. An overcharge detection method for detecting an overcharging of an accumulator according to any one of claims 5 or 6, based on which an overcharging of an accumulator (11) in the said branch (B1, ..., BN) is detected, for a level of charge state determined to be in the first range, as soon as the variation in current identified in the said branch surpasses the first threshold value.
8. An overcharge detection device (1) for detecting an overcharging of an accumulator (11) of a battery (10) comprising a set of parallel branches (B1,..., BN), each branch comprising accumulators disposed in series, the said device being suitable for and capable of collecting the measurements of the currents flowing through the branches of the battery; of identifying at least one variation in current in one branch of the said set of branches with respect to at least one other branch of the said set of branches as a function of the measurements of current collected; of determining a level of state of charge of the said branch; and of detecting an overcharging of an accumulator in the said branch as a function of at least the said variation in current identified and of the level of state of charge determined.
9. An overcharge detection device (1) for detecting an overcharging of an accumulator (11) according to claim 8, suitable for and capable of detecting the said overcharging at least by the testing of at least one condition relative to the variation in current identified, the said condition to be tested relative to the variation in current identified being a function of the level of state of charge determined.
10. An overcharge detection device (1) for detecting an overcharging of an accumulator (11) according to claim 8 or 9, suitable for and capable of calculating a difference between the current measured in the said branch and a reference current determined as a function of at least the current measured in the other branch, of comparing the said difference to a threshold value; and of detecting an overcharging of an accumulator in the said branch (B1,..., BN) based on the result of the said comparison and the level of state of charge determined.
11. An overcharge detection device (1) for detecting an overcharging of an accumulator (11) according to one any one of claims 8 to 10, suitable for and capable of identifying a first variation in current in the said branch at a first time instant and of comparing it with a first threshold value of variation in current, of identifying a second variation in current in the said branch at a second time instant and of comparing it with a second current variation threshold value that is distinct from the first current variation threshold value, and of detecting an overcharging of an accumulator in the said branch (B1,..., BN) as a function of the said first variation in current, of the said second variation in current, and of the level of state of charge determined.
12. An overcharge detection device (1) for detecting an overcharging of an accumulator (11) according to any one of claims 8 to 11, suitable for and capable of, a first range of state of charge levels (ZI) and a second range (ZII), subsequent to the said first range, of state of charge levels of the branch, being defined, detecting an overcharging of an accumulator in the said branch if, the level of state of charge of the branch being in the second range, the variation in current identified in the said branch firstly surpasses a first threshold value and subsequently surpasses a second threshold value, the first and second threshold values having opposite signs.
13. An overcharge detection device (1) for detecting an overcharging of an accumulator (11) according to claim 12, in which the first threshold value is equal to the opposite of the second threshold value.
14. An overcharge detection device (1) for detecting an overcharging of an accumulator according to any one of claims 12 or 13, suitable for and capable of detecting an overcharging of an accumulator (11) in the said branch (B1,..., BN), as soon as the variation in current identified in the said branch surpasses the first threshold value, for a state of charge level determined in the first range.
15. A computer program product comprising instructions which cause the device according to claim 8 to perform the method steps according to claim 1.

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